The taxonomic status of some of New Zealand’s endemic and threatened leiopelmatid frogs has been debated for years. I thus re-examined leiopelmatid diversity by studying the skeletal and external morphology of extinct and extant Leiopelma spp. to determine intra- and inter-specific morphological differentiation. Geographical variation in postcranial element size and shape within the geographically widespread extinct Leiopelma markhami and L. waitomoensis suggest possible extinctions of cryptic taxa, probably after human arrival in the 13th Century. Apart from size, there were no morphological differences between the extant taxa L. archeyi, L. hamiltoni and L. pakeka, but there were morphological differences between these taxa and L. hochstetteri. Relying on morphology and osteology alone is therefore inadequate for identifying species boundaries in extant taxa of Leiopelma. I thus utilised modern and ancient DNA from late Quaternary fossil material to examine the taxonomic diversity of Leiopelma spp. in more detail. Ancient DNA indicated that the extinct L. waitomoensis belongs to the clade comprising extant terrestrial Leiopelma spp., whereas the extinct L. markhami and L. auroraensis form a sister clade to the extant L. hochstetteri. Relatively distinct divergences within the clade representing L. auroraensis and L. markhami, and the formation of clades from the western, and northern South Island, supported my earlier hypothesis that there may have been extinctions of cryptic taxa. Several indeterminate fossils that were collected from the eastern and northern-most North Island were genetically identified as L. archeyi, thereby confirming this taxon’s pre-human distribution for the first time. Molecular results also suggested the synonymisation of the currently recognised extant species L. pakeka and L. hamiltoni. The loss of distinct haplotypes in Leiopelma frogs indicated severe, human-induced genetic bottlenecks. Investigations of microsatellite loci also demonstrated low genetic diversity among contemporary populations. Finally, given that translocations are a primary conservation tool used to maintain genetic diversity in threatened taxa, I utilised a spatially-explicit individual-based, single gene model that assessed the probability of retaining alleles with varying release numbers. Simulations indicated that the release numbers of most translocations of Leiopelma frogs have been adequate to date, with releases of up to 100 frogs being the most preferred option to successfully establish founder populations without compromising the genetic representation, and demographic viability of source populations. Further assessments of genetic diversity, investigations of population parameters, and predicted responses of populations to climate change should now be the focus of Leiopelma frog conservation.